Introduction on DAB/DAB+

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Latest revision as of 21:35, 23 July 2018


[edit] Introduction

DAB, DAB+ and T-DMB European digital radio and mobile television standards share the same transmission system. It's based on OFDM modulation and uses 1.5MHz of spectrum in the VHF television band 3 (or L-band in SHF). A transmitter is broadcasting a set of programmes, called a multiplex or ensemble. The system has been designed for mobile use and is robust up to 300km/h.

With the development of the mmbTools by CRC and opendigitalradio, it is now possible to run a full transmission infrastructure on a laptop running Linux and using a USRP as RF hardware (with gnuradio) or any other similar device.

The transmission chain can be divided in 4 parts:

  • The Encoder encodes the audio source to MPEG-2 Layer II for DAB, MPEG-4 HE-AACv2 for DAB+ or video in MPEG-4 H.264 for T-DMB.
  • The Multiplexer gathers different streams, produces necessary signalling and outputs a single 2048kbit/s stream in ETI format (Ensemble Transport Interface).
  • The Modulator takes the ETI stream and produces a complex I/Q baseband OFDM signal ready for up-conversion to the desired radio frequency.
  • The RF transmission is performed by the USRP, a HackRF One or a similar device.

The ODR-Tools comprises two encoders: Toolame and fdk-aac-dabplus; it includes a multiplexer ODR-DabMux and a modulator ODR-DabMod.

Thanks to the modular approach from these tools it is possible to interface them with other implementations and tools.

[edit] How to get started

[edit] Prerequisites

Let's say you want to learn about DAB transmission and set up a laboratory transmitter that you can use to experiment, gain better understanding, test ideas, evaluate receivers or do measurements.

A will need:

  • Some Linux system knowledge.
  • A recent PC running Debian stable:
  • A USRP (B200, B100, USRP2 and USRP1 are tested to work. The others should be fine too, no guarantees.)
  • To read documentation:
  • To install the required tools on the Debian Linux PC. The Installer scripts will simplify this a lot.
  • Have a look at the example mux and mod configurations in the respective doc/ folders and in mmbtools-aux.
  • And of course, a DAB receiver.

[edit] Step-by-step

The best way to discover these scripts is to start step-by-step. Once you have installed the tools, work your way up from the encoder to the multiplexer, and finally to the I/Q modulator.

  1. Using fdk-aac-dabplus, prepare one or more AAC-encoded .dabp audio files using some .wav files.
  2. Create a configuration file for ODR-DabMux, using doc/example.mux as a base. Use the .dabp files as input and limit the duration of the ETI file to a few thousand frames (a couple of minutes worth of data).
  3. Using ODR-DabMux with this configuration, create a RAW ETI file containing your multiplex.
  4. If you want, compile etisnoop and analyse the ETI file.
  5. Use ODR-DabMod to modulate this ETI file and create an I/Q file.

Once this works, try to get all tools running simultaneously, interconnected using ZeroMQ.

Good luck, and don't transmit without a license !

Other users and developers are reachable on the crc-mmbtools google group:!forum/crc-mmbtools

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